Drift and Wow Correction of Analogue Magnetic Tape Recordings in the Analogue Domain Using HF-Bias Signals

Based on various existing ideas of using the high frequency (HF) bias signal of analogue magnetic tape recordings as a reference signal for irregular speed deviations, this paper discusses the approach to pre-process the bias signal in the analogue domain in a way that allows control of the playback speed of the replay machine in form of a servo loop. Therefore, the bias signal is captured via a sensor head and specifically preprocessed to match the reference frequency of the capstan motor of the tape machine. The machine is set to external vari-speed control mode and, thus, deviations of the bias signal act as external vari-speed reference, allowing automatic speed correction in real-time. The paper discusses the possibilities, problems and limits of the technical implementation of such a prototype.